The goal of the studies proposed here is to increase our understanding of the molecular mechanisms which govern gene expression and cell proliferation in eukaryotes. We are particularly interested in interactions other than the recognition of specific DNA base sequences by proteins, and mechanisms by which nucleosomal DNA can be made more accessible to cellular molecules which interact with DNA. The proposed experiments are based in part on my recent observations that, close to physiological ionic strength, histones interact as octamers with nucleosomes and negatively charged proteins, as well as DNA; and a model acidic protein, polyglutamic acid, promotes the rapid and cooperative assembly of nucleosomes at physiological conditions in vitro. We will ask here, using physical, chemical and biochemical techniques, whether negatively charged proteins (e.g., high mobility group, acidic or phosphorylated nuclear proteins) should be expected to make nucleosomal DNA more accessible, and if dynamic processes in chromatin involving histone octamer displacement can occur, as suggested by this newly discovered property of histones. We will also study and evaluate the usefulness of our novel in vitro chromatin assembly system, and develop a new method for studying nucleohistone complexes that are normally insoluble at physiological ionic strength.